std::optional::value

C++

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Technical Specifications

Utilities library

Type support (basic types, RTTI, type traits)
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initializer_list (C++11)
bitset
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rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=
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strong_order weak_order partial_order strong_equal weak_equal	strong_ordering weak_ordering partial_ordering strong_equality weak_equality	is_eqis_neqis_ltis_lteqis_gtis_gteq
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pair tuple (C++11) apply (C++17) make_from_tuple (C++17)	optional (C++17) any (C++17) variant (C++17)
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swap
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std::optional

Member functions

optional::optional

optional::~optional

optional::operator=

Observers

optional::operator->optional::operator*

optional::operator booloptional::has_value

optional::value

optional::value_or

Modifiers

optional::emplace

optional::swap

optional::reset

Non-member functions

operator==operator!=operator<operator<=operator>operator>=

make_optional

swap

Deduction guides

Helper classes

hash

nullopt_t

in_place_t

bad_optional_access

Helper objects

nullopt

in_place

constexpr T& value() &; constexpr const T & value() const &;	(1)	(since C++17)
constexpr T&& value() &&; constexpr const T&& value() const &&;	(2)	(since C++17)

If *this contains a value, returns a reference to the contained value.

Otherwise, throws a std::bad_optional_access exception.

Parameters

(none)

Return value

A reference to the contained value.

Exceptions

std::bad_optional_access if *this does not contain a value.

Notes

The dereference operator operator*() does not check if this optional contains a value, which may be more efficient than value().

Example

Run this code

#include <optional>
#include <iostream>
int main()
{
    std::optional<int> opt = {};

    try {
        int n = opt.value();
    } catch(const std::exception& e) {
        std::cout << e.what() << '\n';
    }
}

Possible output:

bad optional access

See also

value_or	returns the contained value if available, another value otherwise (public member function)
operator->operator*	accesses the contained value (public member function)
bad_optional_access (C++17)	exception indicating checked access to an optional that doesn't contain a value (class)